(1) Field of the invention.
This invention relates to a steering wheel for a steering mechanism and a method for fabricating the wheel.
(2) Description of the prior art.
Steering wheels having a central hub, spokes and a rim are known in the prior art. In particular, it is known to mold plastic rims around circular metal inserts inside the rims. In preparation for molding, the metal rim insert is placed around the ends of the spokes which are affixed to a central hub. A plastic rim is then formed about the metal rim insert and the ends of the spokes. Although the cost of using a metal rim insert is significant, it has been found that the insert is necessary to maintain the shape of the rim because of shrinkage in the plastic when it cures. If there were no metal rim insert, the shrinkage of the plastic would tend to create a rim with distorted arcs between the ends of the spokes making the rim have the shape of a distorted circle. The use of the metal rim insert maintains the desired circular shape for the rim. Additionally, the use of the metal rim insert guards against the possibility of the plastic rim shrinking to such an extent that the ends of the spokes extend through the rim and are exposed. Using a metal rim insert to maintain the shape of the plastic rim builds stresses into the plastic as it cools. That is, the plastic is not permitted to shrink into a relaxed natural state. Introducing such stresses into a steering rim reduces the strength of the rim and makes it less resilient to impact. Typically, attempts to reduce the magnitude of such shrinkage of the steering rim include using relatively expensive materials that do not shrink very much. For example, ABS plastic is a common material.
The prior art also teaches one piece metal steering wheels including an integral hub, spokes and rim. However, fabrication of such integral pieces is typically difficult. Not only is substantial cost involved, but the configuration of the steering wheel is limited by the complexity of the mold which can be used. Fabrication of complicated shapes can lead to defects in the finished product which are difficult to correct because of their integral structure.